Identify the part of the sentence that contains an error: The museum's revolving doors (A) stopped the crooks (B) as they jam half way round. (C) No error (D)

Introduction / Context:
This question focuses on verb tense consistency in narrative sentences. The context describes an event in the past involving revolving doors and crooks. Learners must identify which part of the sentence violates the tense pattern and therefore contains the error.

Given Data / Assumptions:

Sentence segments: (A) The museum's revolving doors, (B) stopped the crooks, (C) as they jam half way round, (D) No error.

Parts A and B clearly use past tense: "stopped".

Part C uses the present tense form "jam".

The sentence describes a single sequence of past events.

Concept / Approach:

When a sentence narrates a specific incident in the past, all main verbs describing actions in that incident should generally be in the same past tense.

Using a present tense verb like "jam" in the middle of a past narrative creates a tense inconsistency.

The correct past form should be "jammed".

Step-by-Step Solution:
Step 1: Observe part A: "The museum's revolving doors". This is a noun phrase and does not show any tense issue. Step 2: Examine part B: "stopped the crooks". The verb "stopped" is in simple past, which is appropriate for a completed action. Step 3: Examine part C: "as they jam half way round". Here, "jam" is in present tense, which does not match the past tense used in "stopped". Step 4: To maintain consistency, it should read "as they jammed half way round", making both actions clearly past events. Step 5: Therefore, part C is the segment containing the error.

Verification / Alternative check:
Rewriting the sentence completely in correct form gives: "The museum's revolving doors stopped the crooks as they jammed half way round." This form is grammatically consistent and narrates a completed sequence of actions in the past. Any mix of present tense with this past narrative would be inappropriate unless a deliberate stylistic shift is intended, which is not the case in exam questions.

Why Other Options Are Wrong:
Option a is wrong because the noun phrase "The museum's revolving doors" is correct. Option b is wrong because "stopped the crooks" uses correct simple past tense. Option d is wrong because the sentence definitely contains an error in part C, so we cannot mark "No error".

Common Pitfalls:
Some learners overlook tense mismatches when the overall meaning seems clear, but competitive exams require precise grammar. The presence of the word "as" may distract students, but the key is to check the verb forms on both sides of the clause. Practising with many narrative examples helps build an instinct for keeping tenses consistent in sentences.

Final Answer:
The correct answer is: C.